U.S. patent application number 10/052527 was filed with the patent office on 2002-07-25 for focus monitoring method, exposure apparatus, and exposure mask.
Invention is credited to Asano, Masafumi, Fujisawa, Tadahito, Inoue, Soichi, Sakamoto, Takashi, Sato, Takashi, Sutani, Takumichi.
Application Number | 20020100012 10/052527 |
Document ID | / |
Family ID | 26608219 |
Filed Date | 2002-07-25 |
United States Patent
Application |
20020100012 |
Kind Code |
A1 |
Sutani, Takumichi ; et
al. |
July 25, 2002 |
Focus monitoring method, exposure apparatus, and exposure mask
Abstract
According to a focus monitoring method, an exposure mask on
which a focus monitor pattern comprising at least two types of
pattern groups is formed is prepared. A pattern group A of the at
least two pattern groups is illuminated with illumination light
while a barycenter of an illumination light source of illumination
optics is in an off-axis state. At least a pattern group B of the
at least two pattern groups is illuminated with illumination light
while the barycenter of the illumination light source is in an
on-axis state. A positional deviation between the pattern groups A
and B transferred onto a substrate is measured. An effective focus
position can be monitored from this positional deviation.
Inventors: |
Sutani, Takumichi;
(Yokohama-shi, JP) ; Fujisawa, Tadahito; (Tokyo,
JP) ; Sato, Takashi; (Fujisawa-shi, JP) ;
Sakamoto, Takashi; (Zushi-shi, JP) ; Asano,
Masafumi; (Yokohama-shi, JP) ; Inoue, Soichi;
(Yokohama-shi, JP) |
Correspondence
Address: |
Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
1300 I Street, N.W.
Washington
DC
20005-3315
US
|
Family ID: |
26608219 |
Appl. No.: |
10/052527 |
Filed: |
January 23, 2002 |
Current U.S.
Class: |
716/53 ;
250/491.1; 250/492.22; 430/296; 430/30; 430/5 |
Current CPC
Class: |
G03F 7/70641
20130101 |
Class at
Publication: |
716/21 ;
716/19 |
International
Class: |
G06F 017/50 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 24, 2001 |
JP |
2001-015975 |
Mar 27, 2001 |
JP |
2001-090774 |
Claims
What is claimed is:
1. A focus monitoring method of transferring a focus monitor
pattern on a mask illuminated with an electromagnetic wave or
electron beam onto an exposure target substrate by projection
optics, and measuring a shift of the pattern on the substrate,
thereby monitoring an effective focus, comprising: preparing the
mask on which the focus monitor pattern comprising at least two
types of pattern groups is formed; illuminating a pattern group A
of the at least two pattern groups with illumination light while a
barycenter of an illumination light source of illumination optics
is in an off-axis state; illuminating at least a pattern group B of
the at least two pattern groups with illumination light while the
barycenter of the illumination light source is in an on-axis state;
and measuring a positional deviation between the pattern group A
and the pattern group B transferred onto the substrate.
2. The method according to claim 1, wherein said preparing the mask
includes arranging the pattern group A at an arbitrary portion on a
dicing region surrounding a semiconductor device pattern region on
the mask, arranging the pattern group B at another position in the
dicing region to substantially oppose, through the semiconductor
device pattern region, a position where the pattern group A is
arranged, and arranging the pattern group B to be separate from the
pattern group A by a distance substantially corresponding to a
stepping amount with which a stage mounted with the substrate is
sequentially stepped to transfer the mask onto the substrate by the
projection optics, said illuminating the pattern group A with the
illumination light while the barycenter of the illumination light
source is in an off-axis state and illuminating the pattern group B
with the illumination light while the barycenter of the
illumination light source is in an on-axis state includes
sequentially stepping the stage mounted with the substrate, thereby
transferring the mask onto the substrate by the projection optics,
and said measuring the relative positional deviation between the
pattern group A and the pattern group B includes measuring the
positional deviation between the pattern group A which is
transferred onto the substrate after N-time (N is a positive
integer) stepping, and the pattern group B which is transferred
onto the substrate after (N+1)-time stepping.
3. The method according to claim 1, wherein said preparing the mask
on which the focus monitor pattern is formed comprises arranging
the pattern group A and a pattern group C of at least four types of
pattern groups, which comprise the focus monitor pattern comprising
the at least four types of pattern groups, to be close to an
arbitrary portion in a dicing region surrounding a semiconductor
device pattern region on the mask, arranging the pattern group B
and a pattern group D of the at least four types of pattern groups
at another position in the dicing region to substantially oppose,
through the semiconductor device pattern region, a position where
the pattern group A and the pattern group C are arranged, and
arranging the pattern group B and the pattern group D to be
separate from the pattern group A and the pattern group C by a
distance substantially corresponding to a stepping amount with
which a stage mounted with the substrate is sequentially stepped to
transfer the mask onto the substrate by the projection optics, said
illuminating at least the pattern group B with the illumination
light while the barycenter of the illumination light source is in
an on-axis state includes illuminating the pattern group B, C, and
D with the illumination light while the barycenter of the
illumination light source is in an on-axis state, said illuminating
the pattern group A with the illumination light while the
barycenter of the illumination light source is in an off-axis state
and illuminating at least the pattern group B with the illumination
light while the barycenter of the illumination light is in an
on-axis state includes sequentially stepping the stage mounted with
the substrate, thereby transferring the mask onto the substrate by
the projection optics, and said measuring the positional deviation
between the pattern group A and the pattern group B includes
measuring a first positional shift a between the pattern group A
which is transferred onto the substrate after N-time (N is a
positive integer) stepping and the pattern group B which is
transferred onto the substrate after (N+1)-time stepping, measuring
a second positional shift .beta. between the pattern group C which
is transferred onto the substrate after N-time stepping and the
pattern group D which is transferred onto the substrate after
(N+1)-time stepping, and subtracting .beta. from .alpha., thereby
calculating the positional deviation.
4. The method according to claim 3, wherein a combination of the
pattern group A and the pattern group B and a combination of the
pattern group C and the pattern group D are each a combination of a
first and a second pattern group in a box-in-box pattern in which
the first pattern group is surrounded by the second pattern
group.
5. The method according to claim 3, wherein a combination of the
pattern group A and the pattern group B and a combination of the
pattern group C and the pattern group D are each a combination of
line patterns with the same width.
6. The method according to claim 3, wherein said calculating the
positional deviation by subtracting .beta. from .alpha. includes
measuring, as the first positional shift .alpha., a size of a
pattern on the substrate formed by double exposure of the pattern
group A which is transferred onto the substrate after N-time
stepping and the pattern group B which is transferred onto the
substrate after (N+1)-time stepping, measuring, as the second
positional shift .beta., a size of a pattern on the substrate
formed by double exposure of the pattern group C which is
transferred onto the substrate after N-time stepping and the
pattern group D which is transferred onto the substrate after
(N+1)-time stepping, and subtracting .beta. from a, thereby
calculating the positional deviation.
7. The method according to claim 3, wherein said calculating the
positional deviation by subtracting .beta. from .alpha. includes
measuring, as the first positional shift .alpha., a distance
between the pattern group A which is transferred onto the substrate
after N-time stepping and the pattern group B which is transferred
onto the substrate after (N+1)-time stepping, measuring, as the
second positional shift .beta., a distance between the pattern
group C which is transferred onto the substrate after N-time
stepping and the pattern group D which is transferred onto the
substrate after (N+1)-time stepping, and subtracting .beta. from
.alpha., thereby calculating the positional deviation.
8. The method according to claim 1, wherein said illuminating the
pattern group A with the illumination light while the barycenter of
the illumination light source is in an off-axis state includes
arranging a light-shielding body between one region of the mask
corresponding to the pattern group and the illumination light
source, and shielding part of the illumination light that
illuminates the pattern group A.
9. The method according to claim 1, wherein said illuminating the
pattern A with the illumination light while the barycenter of the
illumination light source is in an off-axis state includes
arranging an optical element configured to deflect an optical path
in one direction on that surface of one region of the mask
corresponding to the pattern group A, which opposes the
illumination light source, or in a vicinity thereof.
10. The method according to claim 9, wherein a wedge type
transmitting member or a diffraction grating is used as the optical
element that deflects the optical path in one direction.
11. The method according to claim 1, further comprising
illuminating the pattern group A with illumination light while a
barycenter of an illumination light source is in an off-axis state,
arranging a light-shielding body at a position optically conjugate
to that surface of one region of the mask corresponding to the
pattern group A, which opposes the illumination light source, or in
a vicinity thereof, and shielding part of the illumination light
that illuminates the pattern group A.
12. The method according to claim 11, wherein the optically
conjugate position is a position of a reticle blind in the
illumination optics.
13. The method according to claim 1, wherein said illuminating the
pattern group A with the illumination light while the barycenter of
the illumination light source is in an off-axis state includes
arranging an optical element configured to deflect an optical path
in one direction at a position optically conjugate to that surface
of one region of the mask corresponding to the pattern group A,
which opposes the illumination light source, or in a vicinity
thereof.
14. The method according to claim 13, wherein a wedge type
transmitting member or a diffraction grating is used as the optical
element that deflects the optical path in one direction.
15. The method according to claim 13, wherein the optically
conjugate position is a position of a reticle blind in the
illumination optics.
16. An exposure apparatus which transfers a first and a second
pattern on a focus monitor mask illuminated with an electromagnetic
wave or electron beam onto an exposure target substrate by
projection optics, and measures the first and the second pattern on
the substrate, thereby monitoring an effective focus, comprising:
illumination optics configured to illuminate the first pattern
while a barycenter of an illumination light source is in an on-axis
state, and a component interposed in the illumination optics and
configured to be able to illuminate the second pattern while the
barycenter thereof is in an off-axis state.
17. The exposure apparatus according to claim 16, wherein the
component includes a light-shielding body interposed between the
second pattern and the illumination light source and arranged at a
position optically conjugate to a surface where the second pattern
is formed, or in a vicinity thereof.
18. The exposure apparatus according to claim 17, wherein the
optically conjugate position is a position of a reticle blind in
the illumination optics.
19. The exposure apparatus according to claim 16, wherein the
component includes an optical element, interposed between the
second pattern and the illumination light source and arranged at a
position optically conjugate to a surface where the second pattern
is formed, or in a vicinity thereof, to deflect an optical path in
one direction.
20. The exposure apparatus according to claim 19, wherein the
optically conjugate position is a position of a reticle blind in
the illumination optics.
21. The exposure apparatus according to claim 19, wherein the
optical element to deflect the optical path in one direction is a
wedge type transmitting member or a diffraction grating.
22. An exposure mask comprising: a transparent substrate with a
first and a second major surface, the second major surface opposing
an illumination light source; a first and a second pattern
configured to focus-monitor and formed on the first major surface;
and a component which is arranged on or in the transparent
substrate so as to shield the second pattern with respect to the
illumination light source and which sets a barycenter of the
illumination light source in an off-axis state.
23. The mask according to claim 22, wherein the component
configured to set the barycenter of the illumination light source
in an off-axis state comprises a light-shielding body.
24. The mask according to claim 22, wherein the component
configured to set the barycenter of the illumination light source
in an off-axis state comprises an optical element configured to
deflect an optical path in one direction.
25. The mask according to claim 24, wherein the optical element
configured to deflect the optical path in one direction is a wedge
type transmitting member or a diffraction grating.
26. An exposure mask which transfers a device pattern onto a wafer
through projection optics, comprising: a transparent substrate with
a major surface; the device pattern formed in a pattern region on
the major surface of the transparent substrate; a focus monitor
pattern arranged in a region outside the pattern region on the
major surface of the transparent substrate and formed from two
types of patterns with different diffraction angles; and a
shielding portion which shields one of positive and negative
diffracted light components in two opposing directions which pass
through a pupil of the projection optics and are diffracted by one
pattern of the focus monitor pattern which has a larger diffraction
angle.
27. The mask according to claim 26, wherein the focus monitor
pattern comprises a first pattern group and a second pattern group
which substantially surrounds the first pattern group, and the
first and the second pattern group have a different line width with
respect to each other.
28. The mask according to claim 26, wherein the light-shielding
portion is positioned to pass, of diffracted light from the device
pattern, a light beam passing through the pupil of the projection
optics.
29. The mask according to claim 26, wherein the light-shielding
portion shields one of positive and negative 1st order diffracted
light components from that pattern of the focus monitor pattern
which has the larger diffraction angle.
30. The mask according to claim 26, wherein the focus monitor
pattern comprises a plurality of focus monitor patterns formed at
different distances from the pattern region.
31. The mask according to claim 26, further comprising a pellicle
frame configured to surround the pattern region to protect one
major surface of said transparent substrate, and a protection
member made of a pellicle film configured to seal one end opening
of the pellicle frame, the pellicle frame serving to shield at
least one of the diffracted light components.
32. The mask according to claim 31, wherein a pitch p of that
pattern of the focus monitor pattern which has the larger
diffraction angle satisfies a
relationship:tan.sup.-1(L/H)<cos.sup.-1(.lambda./p)<sin-
.sup.-1(NA/n)where L is a distance from the pattern to the pellicle
frame, H is a height of the pellicle frame, .lambda. is a
wavelength of exposure light of the projection optics, NA is a
wafer side numerical aperture, and n is a magnification.
33. The mask according to claim 26, further comprising a pellicle
frame configured to surround the pattern region in order to protect
one major surface of the transparent substrate, and a protection
member made of a pellicle film configured to seal one end opening
of the pellicle frame, wherein a light-shielding body configured to
shield one of the diffracted light components is provided to part
of the pellicle film.
34. The mask according to claim 33, wherein a pitch p of that
pattern of the focus monitor pattern which has the larger
diffraction angle satisfies a
relationship:tan.sup.-1(L'/H)<cos.sup.-1(.lambda./p)<si-
n.sup.-1(NA/n)where L' is a distance from the pattern to the
light-shielding body adhering to the pellicle film, H is a height
of the pellicle frame, .lambda. is a wavelength of exposure light
of the projection optics, NA is a wafer side numerical aperture,
and n is a magnification.
35. A focus monitoring method comprising: transferring the device
pattern and the focus monitor pattern onto a wafer by using the
exposure mask according to claim 26; measuring a positional shift
produced between the first and the second pattern group of the
focus monitor pattern transferred onto the wafer; and detecting the
positional shift as a defocus.
36. A focus monitoring method employed in transferring a device
pattern onto a wafer through projection optics by using an exposure
mask in which a device pattern is formed in a pattern region on one
major surface of a transparent substrate, comprising: arranging, in
a region outside the pattern region on one major surface of the
transparent substrate, a focus monitor pattern formed from two
types of patterns with different diffraction angles; when
transferring the device pattern onto a sample, shielding one of
positive and negative diffracted light components which pass
through a pupil of the projection optics and are diffracted by one
pattern of the focus monitor pattern which has a larger diffraction
angle; causing a positional shift between the two types of patterns
of the focus monitor pattern on the sample; and detecting the
positional shift as a defocus.
37. The method according to claim 36, wherein a box-in-box pattern
in which inner and outer patterns have different diffraction angles
is used as the focus monitor pattern.
38. The method according to claim 36, wherein said shielding the
diffracted light includes passing, of the diffracted light from the
device pattern, a light beam which passes through the pupil of the
projection optics.
39. The method according to claim 36, wherein said shielding the
diffracted light includes shielding the diffracted light with a
light-shielding body arranged between the exposure mask and the
sample after the diffracted light passes through the exposure mask
and reaches the sample.
40. The method according to claim 36, wherein said shielding the
diffracted light includes using a pellicle frame arranged on the
exposure mask.
41. The method according to claim 40, wherein a pitch p of that
pattern of the focus monitor pattern which has the larger
diffraction angle satisfies a
relationship:tan.sup.-1(L/H)<cos.sup.-1(.lambda./p)<sin-
.sup.-1(NA/n)where L is a distance from the pattern to the pellicle
frame, H is a height of the pellicle frame, .lambda. is a
wavelength of exposure light of the projection optics, NA is a
wafer side numerical aperture, and n is a magnification.
42. The method according to claim 36, wherein said shielding the
diffracted light includes causing a light-shielding body to adhere
to part of a pellicle film arranged on the mask.
43. The method according to claim 42, wherein a pitch p of that
pattern of the focus monitor pattern which has the larger
diffraction angle satisfies a
relationship:tan.sup.-1(L'/H)<cos.sup.-1(.lambda./p)<si-
n.sup.-1(NA/n)where L' is a distance from the pattern to the
light-shielding body adhering to said pellicle film, H is a height
of the pellicle frame, .lambda. is a wavelength of exposure light
of the projection optics, NA is a wafer side numerical aperture,
and n is a magnification.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Applications No.
2001-015975, filed Jan. 24, 2001; and No. 2001-090774, filed Mar.
27, 2001, the entire contents of both of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a focus monitoring method
suitable for focus control of an exposure apparatus used in the
manufacture of semiconductor elements, liquid crystal display
elements, and the like, an exposure apparatus using this focus
monitoring method, and a mask used in this focus monitoring
method.
[0004] 2. Description of the Related Art
[0005] Along with recent device micropatterning, it is becoming
difficult to obtain a sufficiently large process margin such as an
exposure latitude or depth of focus. To prevent a decrease in yield
by effectively using a small process margin, a technique for
monitoring exposure dose and focus more precisely is necessary.
[0006] According to a conventional method of managing focus, a
quality controlling mask with rhombic marks 101 as shown in FIG. 1A
is used. Exposure is performed while changing the focus value. A
focus point where a pattern length Le of a rhombic mark 102, as
shown in FIG. 1B, transferred onto a wafer becomes maximum is
determined as the best focus. In this case, the relationship
between the pattern length Le and defocus is as shown in FIG. 2
(see Jpn. Pat. Appln. KOKAI Publication No. 10-335208).
[0007] At the optimal focus point, even a very small portion of a
rhombic mark is resolved. As defocus proceeds, the resolution for
the small portion decreases. Therefore, the pattern length Le of
the rhombic mark transferred onto the wafer becomes maximum at the
best focus position, and has almost symmetric characteristics
between positive and negative defocus directions. The rhombic mark
can be applied to obtaining the best focus previous to the start of
an exposure process in manufacture.
[0008] The method of this type has the following problems. Assume
that the focus conditions for a manufacturing lot exposed under the
same exposure conditions by using a rhombic mark are to be
controlled. If merely the pattern length Le of the rhombic pattern
after transfer is monitored, (1) the shift direction of the focus
cannot be obtained, and (2) focus monitoring is adversely affected
by variations in exposure dose.
[0009] As another focus monitoring method, a method of detecting a
variation amount of the focus as a positional shift of the pattern
without being adversely affected by the exposure dose has been
proposed (see U.S. Pat. No. 5,300,786).
[0010] The sensitivity of focus detection by means of a mark
according to this method largely depends on the shape of a light
source or a coherence factor a More specifically, with an exposure
condition of a comparatively low .sigma., a sufficiently high
sensitivity may be obtained. However, with a comparatively large
.sigma. condition, which is a generally used condition, or an
annular illumination condition, a sufficiently high sensitivity
cannot be obtained.
[0011] With the above method, when creating the mark, a phase
shifting film must be formed. This increases the load in the mask
formation. Although this method may be applied to a quality
controlling mask, it is difficult to apply it to an actual device
mask.
[0012] Therefore, a focus monitoring method has been sought for
which can measure focus with projection optics at a high
sensitivity and high precision without using a special mask for
focus monitoring.
BRIEF SUMMARY OF THE INVENTION
[0013] According to a first aspect of the present invention, there
is provided a focus monitoring method of transferring a focus
monitor pattern on a mask illuminated with an electromagnetic wave
or electron beam onto an exposure target substrate by projection
optics, and measuring a shift of the pattern on the substrate,
thereby monitoring an effective focus, comprising:
[0014] preparing the mask on which the focus monitor pattern
comprising at least two types of pattern groups is formed;
[0015] illuminating a pattern group A of the at least two pattern
groups with illumination light while a barycenter of an
illumination light source of an illumination optics is in an
off-axis state;
[0016] illuminating at least a pattern group B of the at least two
pattern groups with illumination light while the barycenter of the
illumination light source is in an on-axis state; and
[0017] measuring a positional deviation between the pattern groups
A and B transferred onto the substrate.
[0018] According to a second aspect of the invention, there is
provided an exposure apparatus which transfers a first and a second
pattern on a focus monitor mask illuminated with an electromagnetic
wave or electron beam onto an exposure target substrate by
projection optics, and measures the first and the second pattern on
the substrate, thereby monitoring an effective focus,
comprising:
[0019] illumination optics for illuminating the first pattern while
a barycenter of an illumination light source is in an on-axis
state, and
[0020] a component interposed in the illumination optics and
configured to be able to illuminate the second pattern while the
barycenter thereof is in an off-axis state.
[0021] According to a third aspect of the invention, there is
provided an exposure mask comprising:
[0022] a transparent substrate with a first and a second major
surface, the second major surface opposing an illumination light
source;
[0023] a first and a second pattern configured to focus monitor and
formed on the first major surface; and
[0024] a component which is arranged on or in the transparent
substrate so as to shield the second pattern with respect to the
illumination light source and which sets a barycenter of the
illumination light source in an off-axis state.
[0025] According to a fourth aspect of the invention, there is
provided an exposure mask which transfers a device pattern onto a
wafer through projection optics, comprising:
[0026] a transparent substrate with a major surface;
[0027] the device pattern formed in a pattern region on the major
surface of the transparent substrate;
[0028] a focus monitor pattern arranged in a region outside the
pattern region on the major surface of the transparent substrate
and formed from two types of patterns with different diffraction
angles; and
[0029] a shielding portion which shields one of positive and
negative diffracted light components in two opposing directions
which pass through a pupil of the projection optics and are
diffracted by one pattern of the focus monitor pattern which has a
larger diffraction angle.
[0030] According to a fifth aspect of the invention, there is
provided a focus monitoring method employed in transferring a
device pattern onto a wafer through projection optics by using an
exposure mask in which a device pattern is formed in a pattern
region on one major surface of a transparent substrate,
comprising:
[0031] arranging, in a region outside the pattern region on one
major surface of the transparent substrate, a focus monitor pattern
formed from two types of patterns with different diffraction
angles;
[0032] when transferring the device pattern onto a sample,
performing a process of shielding one of positive and negative
diffracted light components which pass through a pupil of the
projection optics and are diffracted by one pattern of the focus
monitor pattern which has a larger diffraction angle;
[0033] causing a positional shift between the two types of patterns
of the focus monitor pattern on the sample; and
[0034] detecting the positional shift as a defocus.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0035] FIG. 1A shows a rhombic monitor pattern used in conventional
focus monitoring, and FIG. 1B shows a resist pattern obtained by
transferring the rhombic pattern;
[0036] FIG. 2 is a graph showing the relationship between a pattern
length obtained by transferring a rhombic monitor pattern, in the
conventional focus monitoring technique, and a focus obtained at
that time;
[0037] FIG. 3 is a view showing an example of a box-in-box pattern
used in the first embodiment;
[0038] FIG. 4 is a view showing a system configuration that
implements a focus monitoring method according to the first
embodiment;
[0039] FIG. 5 is a view showing the arrangement of two chips
exposed in the first embodiment and focus monitor patterns in
them;
[0040] FIGS. 6A and 6B are views respectively showing the planar
shape of annular illumination which is not light-shielded, and how
light beams irradiate the wafer surface;
[0041] FIGS. 6C and 6D are views respectively showing the planar
shape of annular illumination which is half light-shielded, and how
a light beam irradiates the wafer surface;
[0042] FIG. 7 is a graph showing the relationship between a defocus
and positional shift in the first embodiment;
[0043] FIG. 8 is a view showing a system configuration that
implements a focus monitoring method according to the second
embodiment;
[0044] FIG. 9 is a view showing the layout of focus monitor
patterns exposed onto a wafer in the second embodiment;
[0045] FIG. 10 is a view showing a system configuration that
implements a focus monitoring method according to the third
embodiment;
[0046] FIG. 11 is a view showing the layout of two chips exposed in
the third embodiment and focus monitor patterns in them;
[0047] FIG. 12 is a view showing the layout of two chips exposed in
the fourth embodiment and focus monitor patterns in them;
[0048] FIG. 13 is a sectional view of a mask for explaining the
arrangement of a mask according to the fifth embodiment;
[0049] FIGS. 14A and 14B are sectional views of masks for
explaining the arrangement of masks according to the sixth
embodiment;
[0050] FIG. 15 is a view showing a system configuration that
implements a focus monitoring method according to the seventh
embodiment;
[0051] FIG. 16A is a view showing a system configuration that
implements a focus monitoring method according to the eighth
embodiment;
[0052] FIG. 16B is a view showing the position of illumination
light on a pupil surface in the eighth embodiment;
[0053] FIG. 17 is a view showing another system configuration
according to the eighth embodiment;
[0054] FIGS. 18A and 18B are sectional views of masks for
explaining the arrangement of masks according to the ninth
embodiment;
[0055] FIG. 19 is a sectional view of a mask for explaining the
arrangement of a mask according to the 10th embodiment;
[0056] FIG. 20 is a schematic view for explaining the main part of
an exposure apparatus and diffracted light;
[0057] FIGS. 21A to 21F are plan views showing examples of a
box-in-box type focus monitor pattern used in the above
embodiments;
[0058] FIG. 22 is a partial sectional view of an exposure mask to
show the positional relationship between a focus monitor pattern
and pellicle frame in the 11th embodiment, and shows a case wherein
the 1st order diffraction angle from the focus monitor pattern is
minimum;
[0059] FIG. 23 is a partial sectional view of the exposure mask to
show the positional relationship between the focus monitor pattern
and pellicle frame in the 11th embodiment, and shows a case wherein
the 1st order diffraction angle from the focus monitor pattern is
maximum;
[0060] FIG. 24 is a partial sectional view of the exposure mask to
show the positional relationship between the focus monitor pattern
and pellicle frame in the 11th embodiment, and shows the range of
minimum to maximum 1st order diffraction angles;
[0061] FIG. 25 is a graph showing the relationship between a
positional shift among patterns and a defocus in the 11th
embodiment;
[0062] FIG. 26 is a plan view of a modification of the 11th
embodiment and shows a case wherein a focus monitor pattern is
arranged in a dicing region with a tilt of 45.degree.;
[0063] FIG. 27A is a plan view of another modification of the 11th
embodiment and shows a case wherein a focus monitor pattern is
arranged outside the dicing region;
[0064] FIG. 27B is a plan view of still another modification of the
11th embodiment and shows a case wherein a focus monitor pattern is
arranged outside a dicing region and is arranged on the dicing line
of an adjacent chip by step-and-repeat exposure;
[0065] FIG. 28 is a partial plan view of a mask according to still
another modification of the 11th embodiment and shows a case
wherein focus monitor patterns are arranged in a dicing region
while slightly shifting their positions;
[0066] FIG. 29 is a partial sectional view of an exposure mask
according to the 12th embodiment and shows a case wherein one
component of 1st order diffracted light from a focus monitor
pattern is shielded by part of a specially processed pellicle
film;
[0067] FIG. 30 is a partial sectional view of an exposure mask
according to the 13th embodiment and shows a case wherein one
component of 1st order diffracted light from a focus monitor
pattern is shielded by a light-shielding component attached to an
exposure apparatus;
[0068] FIG. 31 is a plan view of an exposure mask according to the
14th embodiment and shows a case wherein one component of 1st order
diffracted light from a focus monitor pattern is shielded by a
light-shielding component attached to the frame;
[0069] FIG. 32 is a partial sectional view of an exposure mask
according to the 15th embodiment and shows a case wherein a hole is
formed in a pellicle frame and diffracted light from a device
pattern is transmitted through this hole; and
[0070] FIGS. 33A and 33B are views for describing the 16th
embodiment, in which FIG. 33B is a partial sectional view of an
exposure mask, and FIG. 33A is a partial plan view of the exposure
mask to explain the definition of a distance L between a focus
monitor pattern and pellicle frame when the focus monitor pattern
is arranged at an arbitrary position in the dicing region.
DETAILED DESCRIPTION OF THE INVENTION
[0071] Prior to a description of the embodiments, the
characteristic feature of the following first to 10th embodiments
will be described.
[0072] When a focus monitor pattern is illuminated with
illumination light while the barycenter of the illumination light
source is in an off-axis state, a positional shift occurs on a
pattern formed on the sample upon defocusing. When the monitor
pattern is illuminated with illumination light in an ordinary
illumination state wherein the barycenter of the illumination light
source is in an on-axis state, no positional shift upon defocusing
occurs in the pattern formed on the sample.
[0073] A pattern group A is illuminated with illumination light
while the barycenter of the illumination light source is in an
off-axis state. A pattern group B is illuminated with illumination
light in an ordinary illumination state wherein the barycenter of
the illumination light source is in an on-axis state. The positions
of the pattern groups A and B, relative to each other, formed on
the substrate are measured. Then, a defocus can be measured. The
first to 10th embodiments employ this characteristic feature.
[0074] In these embodiments, as a focus monitor pattern, a
box-in-box pattern used in an ordinary misalignment inspection can
be used. When part of the box-in-box pattern is covered with
respect to the illumination light source, the diffracted light
component ratio changes under annular illumination which is used
the most often as the exposure condition, or so-called telecentric
shift can occur. As a result, the position of the box-in-box
pattern to be transferred is shifted upon defocusing. When this
positional shift is measured with a misalignment inspecting
apparatus or the like, the focus value in exposure can be monitored
easily. Hence, focus variation can be measured with high precision
without using a specific pattern such as a phase shifting
pattern.
[0075] The embodiments of the present invention will be described
hereinafter with reference to the accompanying drawing.
First Embodiment
[0076] According to the first embodiment, as the basic arrangement
of a focus monitor pattern, two or more patterns present on one
mask are used. More specifically, as shown in FIG. 3, a box-in-box
pattern widely used in, e.g., alignment inspection, is used. A
means for shielding part of illumination light with respect to an
outer or inner box pattern 301 or 302 of the box-in-box pattern is
used.
[0077] FIG. 4 shows a state wherein a mask 407 is illuminated by
illumination (annular illumination) 401 and the pattern of the mask
407 is transferred onto a chip 409 on a wafer 408 through
projection optics (not shown). As the focus monitor pattern, two
pattern groups, i.e., an inner box pattern 403 (pattern group A)
and inner box pattern 406 (pattern group C), and an outer box
pattern 402 (pattern group B) and outer box pattern 405 (pattern
group D), are respectively arranged on the two ends of the mask
407.
[0078] More specifically, the respective box patterns 402, 403,
405, and 406 are arranged in dicing line regions 411r and 411l
outside a device pattern region 410 of the mask 407.
[0079] The inner box patterns 403 and 406 are arranged in the
dicing line region 411r on the right side of the device pattern
region 410. The outer box patterns 402 and 405 are arranged in the
dicing line region 4111 on the left side of the device pattern
region 410. The box patterns arranged in the dicing line regions
411r and 4111 can be inverted.
[0080] Regarding the inner box pattern 403, a light-shielding body
404 is arranged to shield part of illumination light that
illuminates the inner box pattern 403. More specifically, the
light-shielding body 404 is arranged above the mask surface
opposing the illumination light source 401, to correspond to the
position of the inner box pattern 403. The light-shielding body 404
may be formed in tight contact with the mask 407 so as to be
integral with it. Alternatively, the light-shielding body 404 may
be separated from the mask 407 and held by the exposure
apparatus.
[0081] The patterns are transferred onto the wafer by using this
mask. The practical procedure is as follows. First, the mask 407 is
loaded in the exposure apparatus. The wafer 408 coated with a
resist is introduced into the exposure apparatus. The mask pattern
is transferred onto the wafer 408 by the exposure apparatus in the
step-and-repeat manner as shown in FIG. 4.
[0082] This pattern transfer may be performed either by a stepper
that exposes a mask pattern region at once or by a scanner that
scans the mask pattern region and exposes it. The stepping amount
is determined in accordance with how the device pattern is to be
laid out on the wafer 408.
[0083] When exposure is performed in the above manner, it is done
such that the design centers of the inner box patterns 403 and 406
and those of the outer box patterns 402 and 405 coincide with each
other. More specifically, the following determination in laying out
the two box patterns on the wafer 408 is important. The positions
of the two box patterns must be determined such that, when exposure
is performed by ideal stepping with assumed stepping, the central
positions of the two box patterns coincide with each other and are
exposed on the wafer.
[0084] FIG. 5 is a schematic plan view of chips exposed on the
wafer. Reference numerals 502, 503, 505, and 506 in FIG. 5
respectively denote the transfer patterns of the box patterns 402,
403, 405, and 406 in FIG. 4. The chip region on the left side is
transferred by the Nth exposure operation, while the chip region on
the right side is transferred by the (N+1)th exposure
operation.
[0085] Regarding the pattern 503 exposed with partly shielded
illumination light, its transferred pattern is positionally shifted
upon defocusing due to the reason to be described later. With no
defocus, the transfer pattern 503 should be positioned at 503' in
FIG. 5, where it is overlaid on the center of the outer box pattern
502. Therefore, when the positional shifts of the box-in-box
patterns 502 and 503 formed on the wafer 408 by the patterns 402
and 403 on the mask 407 are measured, focus can be monitored.
[0086] However, the box-in-box patterns are formed by exposure that
takes place across the two chips. Therefore, the positional shifts
of the patterns 502 and 503 include an error caused by a position
precision with which the exposure apparatus is to expose the
respective chips, i.e., by the stepping distortion of the
projection lens.
[0087] For this reason, the box-in-box pattern formed from the
patterns 505 and 506 without using a light-shielding body is
employed as the reference. This pattern does not cause positional
shift with respect to focus. If a defocus should occur, it is
caused by a stepping distortion. When the positional shift of the
box-in-box patterns formed from the patterns 505 and 506 is
measured and the obtained value is subtracted from the positional
shifts of the patterns 502 and 503, then the positional shift is
purely caused by the focus.
[0088] Annular illumination, which is often used in actual exposure
of a device pattern, will be employed as an example, and its effect
will be described. As shown in FIG. 6A, when a focus monitor
pattern is illuminated in a state wherein illumination is not
shielded by a light-shielding body, that is, with ordinary
illumination, the state of the diffracted light on the wafer
surface is as shown in FIG. 6B.
[0089] When the focus monitor pattern used in the first embodiment
has a comparatively large pitch, the ratio of zero order diffracted
light of the diffracted light is very large. Accordingly, it can be
understood that the light beam is represented by the light path of
zero order diffracted light. To facilitate description, FIG. 6A
schematically shows only that portion of annular illumination light
which contributes to resolution and has the highest intensity. Note
that this intensity originally has a distribution.
[0090] In FIG. 6B, the light intensity is obviously axially
symmetrical with respect to the wafer surface. More specifically,
the transferred pattern cannot be positionally shifted with respect
to the focus position.
[0091] In contrast to this, when part of the illumination is
shielded (half is shielded in this example) by the light-shielding
body, as shown in FIG. 6C, the light intensity is no longer
symmetric with respect to the wafer surface. Then, the transferred
pattern is positionally shifted with respect to the focus
position.
[0092] In this manner, when two sets of patterns that behave
differently with respect to the focus are transferred onto the
wafer and their relative positional shift can be measured, accurate
focus monitoring can be performed.
[0093] FIG. 7 shows the result of the first embodiment. The
abscissa represents defocus. The ordinate represents a value
obtained by subtracting the relative positional shift (deviation)
between the patterns 505 and 506 from the relative positional shift
between the pattern 502, obtained without covering the light source
with the light-shielding body, and the pattern 503, obtained by
half-covering the light source with the light-shielding body. From
FIG. 7, it is known that a positional shift of about 20 nm is
measured with respect to a defocus of 0.1 .mu.m, so the defocus can
be sufficiently detected.
[0094] In the first embodiment, annular illumination is used as an
illumination shape. The present invention is not limited to this,
and the same effect can be obtained with an illumination shape
other than annular illumination. In the first embodiment, the
light-shielding body 404 for illumination light is arranged at a
position corresponding to the inner box pattern. The present
invention is not limited to this, and a light-shielding body for
shielding part of the illumination light with respect to the outer
box pattern may be arranged alternatively.
[0095] In this manner, according to the first embodiment, focus
monitoring on the wafer during exposure can be performed with high
precision. A focus monitoring method has conventionally been
available. However, for this purpose, with the conventional method,
a special pattern must be used, or a phase shifting film must be
used. According to the first embodiment, high-precision focus
monitoring can be performed without using such a special mask but
by using an existing mask with a slight improvement. In
measurement, the existing alignment precision measuring apparatus
can be used. Hence, no new apparatus need be particularly used for
this purpose.
[0096] To perform focus monitoring, the illumination is partly
shielded by the light-shielding body with respect to an alignment
precision measurement (focus monitor) pattern. Thus, a positional
shift can be caused with respect to the focus. When this positional
shift is read by an alignment inspecting apparatus, this
measurement directly serves as focus monitoring of the wafer
surface. According to the first embodiment, focus monitoring
becomes easy, and exposure can always be performed with an
appropriate focus. As a result, an increase in yield can be
expected.
Second Embodiment
[0097] FIG. 8 is a view showing a system arrangement that
implements a focus monitoring method according to the second
embodiment of the present invention. Reference numerals 801 to 803,
807 to 810, 811r, and 811l in FIG. 8 correspond to reference
numerals 401 to 403, 407 to 410, 411r, and 411l in FIG. 4. The
second embodiment is different from the first embodiment in that
pattern groups 802 and 803 are formed in one dicing line 811r. Note
that the pattern groups 802 and 803 may be formed in another dicing
line 811l. The pattern groups 802 and 803 do not necessarily form a
box-in-box pattern but can be mere line patterns.
[0098] In the second embodiment, as the basic arrangement of the
focus monitor pattern, two or more pattern groups A (803) and B
(802) present adjacent to each other on one mask are used. A
distance p between the pattern groups A and B is measured in
advance on a mask 807. The pattern group B is exposed in an
ordinary state. When exposing the pattern group A, a
light-shielding body 804 as shown in FIG. 8 is arranged with
respect to the illumination light. Exposure is performed while the
illumination light source is in an off-axis state.
[0099] At this time, when the focus on the wafer surface is
shifted, the pattern groups A and B behave differently due to the
following reason. More specifically, when defocus occurs, the
pattern group A is not positionally shifted by it. On the other
hand, the position of the pattern group B is shifted by defocus,
and the pattern group B is transferred on the wafer with this
shift.
[0100] FIG. 9 shows transfer patterns on a wafer exposed by using
this method. On a chip 909, reference numeral 903 denotes a pattern
obtained by exposing the pattern group A (803). Reference numeral
903' denotes a position where the pattern group A should be
transferred if defocus does not occur. In the second embodiment,
the pattern group A is positionally shifted due to the defocus of
the wafer surface. Reference numeral 902 denotes a pattern obtained
by exposing the pattern group B (802). Off-axis does not occur in
the illumination light that illuminates the pattern group B. Hence,
even if defocus occurs, the pattern 902 is not positionally
shifted.
[0101] The distance between the patterns 902 and 903 on the wafer
is measured. The distance p, by which the patterns 902 and 903 are
originally separated from each other on the wafer, is subtracted,
in the form of a value converted into a value on the wafer, from
the distance. Then, the positional shift of the pattern group A
caused by defocus can be measured. When this positional shift is
obtained, focus monitoring is enabled. As a result, the same effect
as that of the first embodiment can be obtained.
Third Embodiment
[0102] FIG. 10 is a view showing a system configuration that
implements a focus monitoring method according to the third
embodiment of the present invention. Reference numerals 1001 to
1010, 1011r, and 1011l in FIG. 10 correspond to reference numerals
401 to 410, 411r, and 411l in FIG. 4.
[0103] The third embodiment is different from the first embodiment
in that line patterns are used in place of box-in-box patterns.
More specifically, as shown in FIG. 10, line patterns 1003 and 1006
and line patterns 1002 and 1005 are arranged in dicing regions
1011r and 1011l on the two ends of one mask 1007. Note that line
patterns 1003 and 1006 and line patterns 1002 and 1005 may be
arranged in dicing regions 1011l and 1011r. A light-shielding body
1004 is arranged, only with respect to one line pattern 1003 of
these patterns, above that portion of the mask which corresponds to
this pattern. These patterns are arranged such that the line
patterns 1003 and 1006 formed by the Nth exposure operation are
precisely overlaid on the line patterns 1002 and 1005 formed by the
(N+1)th exposure operation, respectively, in accordance with the
step-and-repeat manner.
[0104] Of these line patterns, the line pattern 1003 is
positionally shifted when defocus occurs in the same manner as in
the first embodiment. When defocus occurs, the position of one of
the patterns that are to be originally overlaid is shifted.
Accordingly, the width of a line obtained by exposing two lines in
the overlaid manner increases.
[0105] FIG. 11 shows an example of patterns exposed on the chips on
a wafer. Reference numerals 1102, 1103, 1005, and 1106 in FIG. 11
respectively correspond to the transfer patterns of the patterns
1002, 1003, 1005, and 1006 in FIG. 10. Reference numeral 1103'
denotes a position where the pattern 1103 is formed when defocus
does not occur.
[0106] The factors that change the line width obtained when two
patterns are formed in an overlaid manner include not only defocus
but also a positional shift caused by stepping of the exposure
apparatus, in the same manner as in the first embodiment. Hence, a
change in line width caused by only a change in stepping precision
must be monitored by using the two line patterns 1005 and 1006.
Naturally, no light-shielding bodies are provided for the line
patterns 1005 and 1006. The line widths of the two line patterns
are measured at portions which are exposed in the overlaid
manner.
[0107] The line width of the double exposure portion of the
patterns 1105 and 1006 can change in accordance with stepping. In
addition, the line width of the double exposure portion of the
patterns 1102 and 1003 can change in accordance with focus.
Therefore, when the former line width is subtracted from the latter
line width, variations in line width that depend on only the focus
can be observed. As shown in FIG. 7, if the relationship between
the variations in line width and defocus is obtained in advance,
the focus can be monitored from a change in line width.
Fourth Embodiment
[0108] FIG. 12 describes the fourth embodiment of the present
invention, and is a view showing patterns exposed on a wafer.
Reference numerals 1202, 1203, 1205, and 1206 in FIG. 12 correspond
to reference numerals 1102, 1103, 1105, and 1106 in FIG. 11.
[0109] In the fourth embodiment, an exposure apparatus system
identical to that of FIG. 10 according to the third embodiment is
used. The fourth embodiment is different from the third embodiment
in that exposure is performed without arranging patterns on the two
ends of the mask to be overlaid on each other. Rather, exposure is
performed such that these patterns come to the vicinities of the
patterns of the adjacent chips, as shown in FIG. 12. As the
monitoring method, a distance between the patterns 1202 and 1203 is
obtained. This distance includes both a positional shift caused by
focus and a positional shift caused by stepping of the exposure
apparatus. When the positional shift caused by stepping is obtained
from the distance between the patterns 1205 and 1206 and
subtracting it from the above distance, focus monitoring can be
performed.
[0110] According to the fourth embodiment, focus monitoring can be
performed in the same manner as in the third embodiment. Also, not
the sizes of the patterns but a distance between the patterns is
measured. Hence, the direction of defocus can also be detected.
Fifth Embodiment
[0111] FIG. 13 is a sectional view of a mask used in the focus
monitoring method according to the present invention. Reference
numeral 1301 denotes a light-shielding body; 1302, a focus monitor
pattern; and 1303, a transparent substrate.
[0112] Unlike the means for shielding illumination light in the
first to fourth embodiments, the light-shielding body 1301 for
shielding part of the illumination light is arranged on that
surface of the mask region corresponding to the focus monitor
pattern, which opposes the illumination light source, or in its
vicinity. When the light-shielding body 1301 is arranged on the
mask surface in this manner, part of the illumination light that
should originally be used for exposure of this monitor pattern is
shielded. In other words, an illumination light beam 1304 in FIG.
13 is shielded, and only an illumination light beam 1305 is used
for exposure of this pattern. Hence, the barycenter of the
illumination light source comes off the optical axis, and focus
monitoring as described in the first to fourth embodiments can be
performed.
Sixth Embodiment
[0113] As in the sixth embodiment, in place of shielding part of
the illumination light, an optical element that imparts an angle to
the illumination light may be arranged on that surface of the mask
region corresponding to the focus monitor pattern, which opposes
the illumination light source, or in its vicinity. FIG. 14A is a
sectional view of a mask in the sixth embodiment, in which
reference numeral 1401 denotes an optical element; 1402, a focus
monitor pattern; and 1403, a transparent substrate.
[0114] With the mask of the sixth embodiment, illumination light
that becomes incident from immediately above serves as light 1404
for obliquely illuminating the focus monitor pattern 1402 on the
reticle by the optical element 1401. In other words, by utilizing
the optical element 1401, the focus monitor pattern 1402 can be
illuminated from an oblique direction. Hence, the same effect as
that of the fifth embodiment can be obtained, and focus monitoring
can be performed.
[0115] In FIG. 14A, a wedge type optical element is used. However,
the present invention is not limited to this, and a grating type
optical element as shown in FIG. 14B may be used instead.
Seventh Embodiment
[0116] In the fifth embodiment, a light-shielding body used for a
focus monitor pattern is arranged on that surface of the mask which
opposes the illumination light source. The same effect as this can
be obtained when the light-shielding body is arranged at another
place.
[0117] FIG. 15 is a schematic view of the seventh embodiment.
Reference numeral 1501 in FIG. 15 denotes a light-shielding body;
1502, a reticle blind surface; 1503, the projection lens of
illumination optics; 1504, a mask; 1505, a focus monitor pattern;
1506, the projection lens of projection optics; 1507, a wafer
surface; and 1508, illumination light, respectively.
[0118] According to the seventh embodiment, the light-shielding
body 1501 is arranged in the vicinity of the reticle blind surface
1502 which is almost optically conjugate to that surface of the
mask 1504 which opposes the illumination light source. The box
pattern 1505 identical to that described in the first embodiment,
or a focus monitor pattern identical to that described in the third
embodiment is illuminated. The light-shielding body 1501 has a
function equivalent to that of the light-shielding body 1301 of the
fifth embodiment. Thus, the same effect as that of the fifth
embodiment can be obtained, and focus monitoring can be
performed.
[0119] The light-shielding body 1501 can be provided as a
constituent component of the exposure apparatus. If the size and
installation place of the focus monitor pattern are standardized,
the light-shielding body 1501 provided standard to the exposure
apparatus can be shared by various types of masks. Alternatively,
the light-shielding body 1501 may be exchanged for each mask.
[0120] In the seventh embodiment, the light-shielding body is
arranged near the reticle blind surface. However, the present
invention is not limited to this, and the light-shielding body may
be arranged at any other place as far as it is optically
conjugate.
Eighth Embodiment
[0121] In the seventh embodiment, focus monitoring is enabled by
arranging the light-shielding body in the vicinity of the reticle
blind surface. Focus monitoring is enabled also by arranging an
optical element like one used in the sixth embodiment on the
reticle blind surface.
[0122] FIG. 16A shows the schematic arrangement of the eighth
embodiment. Reference numerals 1601 to 1608 in FIG. 16A correspond
to reference numerals 1501 to 1508 in FIG. 15. Reference numeral
1609 denotes illumination light inclined by an optical element
1601.
[0123] When illumination light corresponding to a focus monitor
pattern 1605 is inclined by the optical element 1601 arranged in
the vicinity of a reticle blind surface 1602 almost conjugate to
that surface of a mask 1604 which opposes the illumination light
source, the same effect as that of the seventh embodiment can be
produced.
[0124] FIG. 16B shows the position of illumination light on the
pupil surface. In FIG. 16B, the illumination is annular
illumination. Reference numeral 1610 denotes the aperture of the
projection lens. When the central position of the illumination
light is shifted from the central position of the aperture of the
projection lens to, e.g., the position 1612 with respect to a
position 1611 of the illumination light that must originally be
transmitted through the pupil surface, a light intensity
distribution asymmetric with the wafer surface as shown in FIG. 6C
can be formed. Since the monitor pattern is positionally shifted
with respect to the focus, focus monitoring can be performed.
[0125] In FIG. 16A, a wedge type optical element is used. However,
the present invention is not limited to this, and a grating type
optical element as shown in FIG. 17 may also be used instead.
Reference numerals 1701 to 1709 in FIG. 17 respectively correspond
to reference numerals 1601 to 1609 in FIG. 16.
[0126] The light-shielding body 1601 can be provided as a
constituent component of the exposure apparatus. If the size and
installation place of the focus monitor pattern are standardized,
the light-shielding body 1601 provided standard to the exposure
apparatus can be shared by various types of masks. Alternatively,
the light-shielding body 1601 may be exchanged for each mask.
[0127] In the eighth embodiment, the optical element is arranged
near the reticle blind surface. However, the present invention is
not limited to this, and the optical element may be arranged at any
other place as far as it is optically conjugate.
Ninth Embodiment
[0128] In the seventh embodiment, a light-shielding body is
arranged on that surface of the mask which opposes the illumination
light source, to shield part of illumination light to the focus
monitor pattern. In this case, an influence on a device pattern
present on the same mask must also be considered. More
specifically, if light which should be used for exposure of the
device pattern is shielded, it may largely influence the device
pattern that should originally be exposed in the normal manner.
Therefore, this focus monitoring method must be performed while
avoiding an influence on the device pattern.
[0129] FIG. 18A shows an example of a sectional view of the mask.
In FIG. 18A, reference numeral 1801 denotes a light-shielding body;
1802, a focus monitor pattern; 1803, a transparent substrate; and
1806, a device pattern present on the mask. The positional
relationship between the light-shielding body 1801, focus monitor
pattern 1802, and device pattern 1806 is as shown in FIG. 18A. The
edge of the light-shielding body 1801 is to correspond to the
central position of the focus monitor pattern 1802.
[0130] To prevent the illumination light that is to expose the
device pattern from being shielded by the light-shielding body
1801, the focus monitor pattern 1802 must be moved from the endmost
portion of the device pattern and arranged at a position where the
following equation (1) is satisfied:
Lg>w.times.tan .theta. (1)
[0131] where Lg is the distance from the device pattern to the
box-in-box pattern, W is the thickness of the mask, and .theta. is
the illumination angle in the mask member. The illumination angle
.theta. is an angle determined by sin .theta.=NA/nM where NA is the
wafer side numerical aperture of the projection lens, n is the
refractive index of the mask material (usually SiO.sub.2) for
exposure light, and M is the magnification of the mask.
[0132] If this condition is not satisfied, the mask becomes as
shown in FIG. 18B. Then, the illumination light that should expose
the device pattern is also shielded by the light-shielding body
1801 on the lower surface of the box pattern. If equation (1) is
satisfied, focus monitoring can be performed so as not to adversely
affect the device pattern at all.
10th Embodiment
[0133] In the fifth embodiment, the light-shielding body is
arranged on that surface of the mask which opposes the illumination
light source, in order to shield light to the box pattern. To
eliminate any adverse affect on the device pattern, equation (1)
must be satisfied (FIG. 18A). However, as the thickness of the mask
is determined, the focus monitor pattern must be separated from the
device pattern region by at least W.times.tan .theta.. This leads
to an increase in chip area. To reduce the chip area, this distance
may be minimized.
[0134] FIG. 19 shows a sectional view of a mask according to the
10th embodiment to show its arrangement. In FIG. 19, reference
numeral 1901 denotes a light-shielding body; 1902, a focus monitor
pattern; 1903, a transparent substrate; and 1906, a device pattern
present on the mask. As shown in FIG. 19, if the light-shielding
body 1901 can be buried in the transparent substrate 1903 or in the
substrate, W of equation (1) decreases. The focus monitor pattern
can be accordingly arranged closer to the device pattern region by
an amount corresponding to this decrease.
[0135] When this mask is used, focus monitoring can be performed
with the distance Lg between the device pattern and focus monitor
pattern being further decreased. This leads to a reduction in chip
area.
[0136] As described above in detail, according to the first to 10th
embodiments, the focus monitor pattern group A formed on the mask
is illuminated with illumination light while the barycenter of the
illumination light source is in an off-axis state. Another pattern
group B is illuminated with ordinary illumination light while the
barycenter of the illumination light source is in an on-axis state.
The positions of the pattern groups A and B, formed on the
substrate, relative to each other may be measured, thereby
measuring defocus. In this case, the focus of the projection optics
can be measured with high sensitivity and high precision without
using a specific mask for focus monitoring.
[0137] In the first to 10th embodiments, the illumination light for
part of the focus monitor pattern is in an off-axis state, to cause
a pattern shift, thereby performing focus monitoring. The method of
causing a pattern shift is not limited to that described in the
above embodiments. Other methods of causing a pattern shift will be
described in the following 11th to 16th embodiments. Prior to
description of the practical embodiments, the characteristic
feature that is common among the following embodiments will be
described.
[0138] The pattern used in the following embodiments is formed by
altering part of a pattern used in alignment precision measurement,
e.g., a box-in-box pattern also used in the first embodiment. The
position of this pattern is appropriately set with respect to the
actual device pattern. This is the characteristic feature of the
following embodiments.
[0139] FIG. 20 shows an optics in a general exposure apparatus.
Referring to FIG. 20, reference numeral 2001 denotes an
illumination light source; and 2002, a condenser lens. The
condenser lens 2002 is the main element of the illumination optics.
Reference numeral 2003 denotes an exposure mask; 2004, a reduction
projection lens as the main element of the projection optics; 2005,
a pupil surface; and 2006, a wafer. Light emitted from the
illumination optics to irradiate the exposure mask 2003 is
diffracted by the mask surface and is divided into zero order light
2010, +1st order light 2011, -1st order light 2012, and the
like.
[0140] Under the illumination condition symmetric with respect to
the optical axis, assume a case wherein a telecentric shift does
not exist and those components of the diffracted light which are
concerned in pattern formation are +1st order light, zero order
light, and -1st order light. Also assume a case wherein the
illumination is not shielded by other than the pupil surface of the
projection optics but entirely reaches the wafer. As far as no
telecentric shift is present, even if the focus position is
shifted, the pattern to be transferred is not positionally
shifted.
[0141] However, of positive and negative diffracted components, if
only one diffracted component (e.g., the +1st order light) can be
shielded by some means before it reaches the wafer, the ratio of
the two-beam interfering components of the zero order light and
-1st order light to the two-beam interfering components of the zero
order light and +1st order light on the wafer changes. Thus, when
defocus occurs, it can be detected as a positional shift of the
pattern.
[0142] By utilizing the two effects described above, in the
following embodiments, an actual device pattern is arranged at a
position where it does not shield the diffracted light, and the
focus monitor pattern is arranged at a position where it shields
the diffracted light, or is processed to shield the diffracted
light. With the above arrangement, if the positional shift of the
focus monitor pattern is measured with an alignment precision
measuring apparatus, defocus can be easily measured with high
precision.
[0143] More specifically, as the focus monitor pattern, a
box-in-box pattern is used. Of inner and outer patterns, one is
formed with a small pitch, while the other is formed with a large
pitch. The diffraction angle of the diffracted light from the
small-pitch pattern is larger than that of the diffracted light
from the large-pitch pattern. Hence, the pitches are set such that
the former diffracted light is shielded while the latter diffracted
light is not shielded. In other words, with the former diffracted
light, a positional shift is caused by defocus. With the latter
diffracted light, a positional shift is not caused by defocus.
[0144] Then, when defocus occurs, only one pattern is positionally
shifted. Therefore, focus monitoring can be performed by detecting
a shift between the inner and outer patterns. In addition, when the
focus monitor pattern is arranged outside a region where the device
pattern is formed, focus monitoring described above can be
performed without limiting the device pattern region at all.
[0145] Therefore, according to the following embodiments, the focus
of the projection optics can be measured with high sensitivity and
high precision without using a specific mask for focus monitoring.
The embodiments of the present invention will be described with
reference to the accompanying drawings.
11th Embodiment
[0146] In the 11th embodiment, as a focus monitor pattern, a
box-in-box pattern mark with which a positional shift can be
detected by an alignment precision measuring apparatus is used.
This mark is partly improved to have a focus detection effect, and
the arrangement of the mark itself is devised.
[0147] FIGS. 21A to 21F are plan views of focus monitor patterns
used in the 11th embodiment. Each focus monitor pattern is
constituted by an outer large-width large box mark (pattern) 2301
and a small box mark (pattern) 2302. The large box mark 2301 has an
opening. The small box mark 2302 is formed inside the opening and
is made from fine patterns.
[0148] The large box mark 2301 may have a predetermined width, as
shown in FIG. 21A, or have an opening in the light-shielding
surface, as shown in FIG. 21B. In FIG. 21A, a plurality of
large-width patterns may be concentrically formed.
[0149] The small box mark 2302 inside the large box mark 2301 may
form a line-and-space (L/S) pattern with thin square patterns, as
shown in FIGS. 21A and 21B, may be formed from a simple L/S
pattern, as shown in FIG. 21C, or may be formed from a checkered
pattern, as shown in FIG. 23D.
[0150] As an improvement of the focus monitor pattern, one in which
the inner and outer patterns are inverted, as shown in FIGS. 21E
and 21F, may be used. More specifically, an outer large box mark
2301 may be formed from fine patterns (L/S or checkered pattern),
and an inner small box mark 2302 may be formed from large-width
patterns (a rectangle with a large area).
[0151] In the following description, the outer large box mark 2301
is formed from large-width patterns, and the inner small box mark
2302 is formed from fine patterns, as shown in FIGS. 21A to
21D.
[0152] In the focus monitor pattern as shown in each of FIGS. 21A
to 21D, of .+-.1st order light components (1st order light
components with positive and negative signs) from the inner small
box mark 2302, if only one can be shielded by some means, the ratio
of the two-beam components of the zero order light and +1st order
light to the two-beam components of the zero order light and -1st
order light on the wafer changes. Thus, when the focus position is
shifted, the pattern itself is positionally shifted, and the
positionally shifted pattern is transferred onto the wafer.
[0153] Conversely, as the outer large box mark 2301, a
comparatively large pattern designed so the diffracted light is not
shielded by it is employed. With this setting, the relative shift
of the two transfer patterns is measured by using the alignment
precision measuring apparatus. Thus, a defocus amount can be
detected easily.
[0154] When, however, the two diffracted light components from the
device pattern on the exposure mask are shielded simultaneously,
while the focus precision can be measured, the image forming
characteristics of the device pattern itself, which is crucial, may
be adversely affected. Hence, a countermeasure must be taken with
which only one of the two 1st order diffracted light components
from the small box mark of the box-in-box pattern, which is the
focus monitor pattern, is shielded without shielding the diffracted
light from the device pattern. This countermeasure will be
described.
[0155] According to the eleventh embodiment, as a means for
shielding only one of the 1st order diffracted light components
from the small box mark of the box-in-box pattern, a pellicle frame
is utilized. The pellicle frame supports a pellicle film that
protects the surface of the exposure mask. The exposure mask
generally serves for exposure with the pellicle film being attached
to it. With a pellicle frame, no new process need be introduced in
mask fabrication, and the cost does not increase.
[0156] FIG. 22 shows, together with a partial sectional view of an
exposure mask, the positional relationship between a device pattern
2604 and box-in-box type focus monitor pattern 2605, and that
between a pellicle frame 2608 and pellicle film 2609. In FIG. 22,
reference numeral 2600 denotes a transparent substrate which is
transparent with respect to exposure light; 2601, a pattern region
where an actual device pattern is present; 2602, a dicing region
where the focus monitor pattern 2605 and an alignment mark are
present; and 2603, a periphery where the mask alignment mark is
arranged.
[0157] The focus monitor pattern 2605 is indicated by the outer
shape of the section (or side surface) of an outer large box
pattern 2301 (FIG. 21A). The focus monitor pattern 2605 has an
inner small box pattern 2302 (FIG. 21A) in it, although its
detailed illustration is omitted.
[0158] According to the 11th embodiment, the focus monitor pattern
2605 is arranged at the outermost portion of the dicing region
2602. Diffracted light from the dicing region 2602, which is
effective for forming an image, is not shielded by the pellicle
frame 2608. Only light from the inner pattern of the focus monitor
pattern 2605 is shielded. The practical procedure of determining
this arrangement will be described as follows.
[0159] In the exposure apparatus, the numerical aperture (NA) is
determined in advance. When an n-time mask is used, the maximum
diffraction angle (.theta.p) of the 1st order diffracted light is
limited to satisfy sin .theta.p=NA/n. In other words, even when the
1st order diffracted light is diffracted at an angle of .theta.p,
i.e., sin .sup.-1(NA/n), or more, it can not transmit through the
pupil of the projection optics. Hence, the maximum diffraction
angle need not be considered here.
[0160] Assume a case wherein the diffracted light 2607 from the
small box mark of the focus monitor pattern 2605 is to be shielded
by the pellicle frame 2608. If the height H of the pellicle frame
2608 is determined, the position at which the pellicle frame 2608
does not shield diffracted light 2606 from the pattern region 2601
is determined. This position is shown in FIG. 22 in the form of the
distance from the end of the dicing region 2602 to the pellicle
frame 2608, and its minimum distance is expressed by L.sub.fMIN.
Conversely, if this distance is larger than L.sub.fMIN, the 1st
order diffracted light 2606 from the pattern region 2601 is not
shielded by the pellicle frame 2608.
[0161] To shield the 1st order diffracted light from the small box
mark involved in the monitor pattern 2605, the height H of the
pellicle frame 2608, L.sub.fMIN, and the minimum diffracted angle
.theta..sub.fMIN of the diffracted light from the small box mark
may satisfy a relation tan .theta..sub.fMIN>L.sub.fMIN/H.
[0162] From the above description, the small box mark may be formed
from fine patterns so that the 1st order diffracted light is
diffracted within a range where
tan.sup.-1(L.sub.fMIN/H)<.theta..sub.fMIN<sin.sup.-1(- NA/n)
is established.
[0163] This condition of angle will be studied from the viewpoint
of the pitch of the small box mark. Generally, the relationship
between light diffracted by a diffraction grating (corresponding to
a mask pattern in this case) and the diffraction angle satisfies d
cos .theta.=m.lambda. where .theta. is the diffraction angle, d is
the pitch of the mask pattern, .lambda. is the exposure wavelength,
and m is the order of diffraction. As the order of diffraction,
only 1st order will be considered in this case. Hence, this
equation becomes cos .theta.=.lambda./d when m=1. When this result
is further substituted in the above equation of condition about the
diffraction angle .theta..sub.f from the small box mark, it
yields:
tan.sup.-1(L.sub.fMIN/H)<cos.sup.-1(.lambda./d)<sin.sup.-1(NA/n)
(2)
[0164] If the pattern pitch is set to satisfy this condition, the
diffracted light from the device pattern 2604 is not shielded, and
only one component of the 1st order diffracted light from the small
box pattern can be shielded.
[0165] Assuming that the pitch of the small box mark is determined
to a certain constant value within the above range, the position
where the pellicle for shielding only the 1st order diffracted
light beam from such small box mark will be considered. FIG. 22
shows a case wherein the diffraction angle satisfying this
condition is minimum (.theta..sub.fMIN) FIG. 23 shows a case
wherein this angle becomes maximum. In FIG. 23, diffracted light
beams 2606 and 2607 respectively from the device pattern 2604 and
the small box pattern become parallel to each other. In other
words, as the intermediate condition between FIGS. 22 and 23, if
the inner wall of the pellicle frame 2608 is between A and B, that
is, within a width Ld of the dicing region, then only one of the
two 1st order diffracted light components from the small box mark
can be shielded. Thus, this mask can be employed as the focus
monitor mask.
[0166] More specifically, the distance L from the focus monitor
pattern 2605 to the pellicle frame 2608 satisfies:
[0167] L.sub.fMIN<L<L.sub.fMAX=L.sub.fMIN+Ld (3)
[0168] That is, L may be set to fall within the range of L.sub.fMIN
to L.sub.d.
[0169] A practical application will be described below. The
exposure conditions used here are: exposure wavelength .lambda.=248
nm, wafer-side numerical aperture NA=0.68, illumination coherence
factor .sigma.=0.75, and the mask pattern magnification was 4. The
box-in-box type focus monitor pattern 2605 shown in FIG. 21A was
arranged on the end of the dicing region 2602 of the employed
exposure mask. The width of the dicing region 2602 was 80 .mu.m
(when converted into a size on the wafer). In the following
description, the size is the one converted into a size on the
wafer, unless otherwise noted.
[0170] The width of the outer box mark was 2 .mu.m, and the width
of the inner box mark was 2 .mu.m. The inner box mark was formed
from 0.3-.mu.m L/S patterns with a pitch that satisfies equation
(2). The height H of the employed pellicle frame 2608 was 6 mm (on
the mask). The pellicle frame 2608 was arranged at, as a position
that satisfies equation (2), a position at a distance of 1 mm (on
the mask) from the focus monitor pattern 2605.
[0171] First, the detection sensitivity when actual exposure was
performed by using the exposure mask was obtained. A coating type
anti-reflection film was formed on an Si wafer to a thickness of 60
nm by spin coating and heating. A chemically amplified positive
resist was formed by spin coating to a thickness of 0.4 .mu.m.
After that, prebaking was performed at 100.degree. C. for 90 sec.
This series of processes was performed in a coater and developer
connected to the exposure apparatus. The wafer that had undergone
this process was transferred to the exposure apparatus, and was
exposed by using the exposure mask.
[0172] During exposure, the preset exposure dose of the exposure
apparatus was changed between four values, i.e., 17.5 mJ/cm.sup.2,
20 mJ/cm.sup.2, 22.5 mJ/cm.sup.2, and 25 mJ/cm.sup.2. Defocus was
changed from -0.5 .mu.m to +0.5 .mu.m with a pitch of 0.1 .mu.m.
The exposed focus monitor pattern was subjected to the alignment
precision measuring apparatus to measure the defocus dependency of
the positional shift between the center of the outer box mark and
the center of the inner box mark.
[0173] FIG. 25 shows the relationship between the positional shift
and defocus of this case. From FIG. 25, the positional shift does
not depend on the exposure dose, and a defocus of 0.1 .mu.m
corresponds to a positional shift of 10 nm. The reproducibility of
the alignment precision measuring apparatus used in this case is
2.5 nm. When this value was converted into a focus precision, the
focus monitor pattern used in this case could realize a high focus
detection sensitivity of 25 nm. The influence on the device pattern
was also studied. A pattern closest to the focus monitor pattern
and a pattern close to the center of the mask were compared. No
problem was observed concerning the transfer precision.
[0174] As described above, when the pellicle frame was placed at
that position which satisfies the above conditions (equations (2)
and (3)), the focus precision could be detected as a positional
shift of the pattern without adversely affecting the device pattern
at all. In an actual measurement, the relative shift between the
outer and inner box marks may be measured by using an alignment
inspecting apparatus. The defocus, including its direction, could
be obtained with high detection sensitivity without using a special
mask technique like the conventional one that uses a phase shift
mask.
[0175] With the exposure mask employed in this case, a box-in-box
type focus monitor pattern was used. However, the present invention
is not limited to this. It suffices as far as conditions, with
which part of a mark detectable by the alignment precision
measuring apparatus shields the diffracted light described above,
are obtained. Inverted patterns of FIGS. 21A to 21F may also be
employed.
[0176] Assume that the dicing region is narrow and it is difficult
to arrange the pellicle frame without adversely affecting the
device pattern. In this case, as shown in FIG. 26, a focus monitor
pattern 2605 may be arranged on the corner of the mask. Then, the
distance from a pattern region 2601 to this focus monitor pattern
2605 becomes about 1.4 times. Therefore, the position precision of
a pellicle frame 2608 can be moderated.
[0177] As shown in FIG. 27A, a focus monitor pattern 2605 may be
arranged on a further outside portion of a dicing region 2602,
which does not overlap with the device region of the adjacent chip.
Exposure may be performed by setting the exposure region to a
region including a focus monitor pattern 2605. In this case, since
the distance from the device pattern region 2601 to the pellicle
frame (not shown; refer to 2608 in FIG. 22) increases, the position
precision of the pellicle frame can be moderated effectively.
[0178] FIG. 27B shows a state wherein the mask pattern of FIG. 27A
is formed on a wafer in a step-and-repeat manner. In this case, a
focus monitor pattern 2605 is exposed onto a dicing region 2602 of
an adjacent chip.
[0179] In the 11th embodiment, the focus monitor pattern and the
device pattern are arranged on one mask. Alternatively, the focus
monitor pattern may be arranged on a quality control reticle or the
like which is used to control the state of the apparatus. Assume
that the relative position precision between the pellicle frame and
focus monitor pattern is strict. In this case, as shown in, e.g.,
FIG. 28, a large number of focus monitor patterns 2605 may be
arranged to be slightly displaced from each other. After
inspection, as a focus monitor pattern, one focus monitor pattern
2605 that exhibits a desired performance (i.e., one satisfying the
relation of equation (3)) may be used.
[0180] In this manner, according to the 11th embodiment, to measure
the defocus, of the .+-.1st order light components from the small
box mark of the focus monitor pattern, only one is shielded. Thus,
the focus precision on the wafer can be measured with high
precision as a positional shift. This allows exposure with a
constantly appropriate focus, contributing to an increase in
yield.
[0181] A method of measuring the focus precision has conventionally
been available. However, for this purpose, with the conventional
method, a special pattern must be used, or a phase shifting film
must be used. According to the 11th embodiment, the focus precision
can be measured without using such special mask but by using an
existing mask with a slight improvement. In measurement, the
existing alignment precision measuring apparatus can be used.
Hence, no new apparatus need be particularly used for this
purpose.
12th Embodiment
[0182] FIG. 29 is a sectional view showing the arrangement of the
main part of an exposure mask according to the 12th embodiment. In
the following embodiment, portions that are identical to those of
FIG. 22 are denoted by the same reference numerals as in FIG. 22,
and a repetitive description will be omitted.
[0183] In the 11th embodiment, the 1st order diffracted light from
the box-in-box pattern is shielded by the pellicle frame 2608. Any
means can be used as far as it can shield only one of the two
diffracted light components. Regarding this, a pellicle film 2609
for transmitting light originally used for exposure is divided into
regions, and the divisional regions are selectively colored. Thus,
the pellicle film 2609 is divided into a portion for transmitting
light used for exposure and a portion for not transmitting light.
Only one of two diffracted light components 2607 from the small box
mark is shielded by a colored portion 2610 of the pellicle film
2609. Diffracted light 2606 from a device pattern 2604 is
transmitted through the pellicle film 2609.
[0184] In this manner, according to the 12th embodiment, some
region of the pellicle film 2609 is colored to form the portion
2610 that does not transmit light. Thus, only one of two components
of the diffracted light 2607 from the small box mark of a focus
monitor pattern 2605 can be shielded. Therefore, the focus
precision can be measured in the same manner as in the case of the
11th embodiment. The same effect as that of the 11th embodiment can
be obtained.
13th Embodiment
[0185] FIG. 30 is a sectional view showing the arrangement of the
main part of an exposure mask according to the 13th embodiment. In
the 13th embodiment, a light-shielding member 2710 for shielding
only one of two 1st order diffracted light components from the
box-in-box pattern is arranged at an appropriate position in an
exposure apparatus. This is particularly effective when the
diffracted light cannot be shielded by a pellicle frame 2608 or
pellicle film 2609 due to some limitation posed in mask
fabrication.
[0186] With the method of the 13th embodiment as well, only one of
the two components of 1st order diffracted light 2607 from the
small box mark of a focus monitor pattern 2605 can be shielded.
Hence, the focus precision can be measured in the same manner as in
the 11th embodiment.
14th Embodiment
[0187] FIG. 31 is a plan view showing the arrangement of the main
part of an exposure apparatus according to the 14th embodiment. A
case is assumed wherein, unlike in the 13th embodiment, a pellicle
frame 2608 for shielding only diffracted light from a box-in-box
pattern cannot be arranged at a predetermined position. More
specifically, in this case, an alignment mark on the mask is
present near the outer side of the mask substrate. Since the
pellicle frame 2608 must surround the pattern on the mask entirely,
it must surround not only the pattern region but also the alignment
mark on the mask.
[0188] In this case, if a focus monitor pattern 2605 of a dicing
region 2602 is not present near the reticle alignment mark, a
special component 2810 is added to the pellicle frame 2608 to
shield one of the two components of 1st order diffracted light 2607
from the small box mark. Thus, even when the pellicle frame 2608
cannot be arranged at a position where it shields one of the two
components of the 1st order diffracted light 2607 from the small
box mark, only the diffracted light can be shielded by the
component 2810. Therefore, with the method of the 14th embodiment,
the same effect as that of the 11th embodiment can be obtained.
15th Embodiment
[0189] FIG. 32 is a sectional view showing the arrangement of the
main part of an exposure mask according to the 15th embodiment. In
contrast to the cases of the 13th and 14th embodiments, when a
pellicle frame 2608 is too close to a pattern region 2601, two
diffracted light components 2606 and 2607 respectively from a
device pattern 2604 and focus monitor pattern 2605 may be shielded
by the pellicle frame 2608. In this case, a hole may be formed in
that portion of the pellicle frame 2608 which shields the
diffracted light from the device pattern 2604, to transmit this
diffracted light. Naturally, the 1st order diffracted light 2607
from the small box mark of the focus monitor pattern 2605 must be
limited to such a height that it can be shielded.
[0190] With the 15th embodiment as well, only one of the two
components of the 1st order diffracted light 2607 from the small
box mark of the focus monitor pattern 2605 can be shielded. The
diffracted light from the device pattern 2604 can be transmitted.
Thus, the same effect as that of the 11th embodiment can be
obtained.
16th Embodiment
[0191] FIG. 33B is a sectional view showing the arrangement of the
main part of an exposure mask according to the 16th embodiment. In
the 11th embodiment, the focus monitor pattern is arranged at the
endmost portion of the dicing region, and various types of
conditions are obtained. However, the present invention is not
limited to this. As shown in FIG. 33A, a value which is simply set
to Ld in the 11th embodiment may be replaced with Le=Ld-x/2-y where
Ld is the length of the dicing region itself, x is one side of the
small box mark of a focus monitor pattern 2605, and y is the
distance from the center of the focus monitor pattern 2605 to the
end of a dicing region 2602. Then, the focus precision can be
measured by this mask with the same conditions as those of the 11th
embodiment.
[0192] In FIG. 22, in order to facilitate understanding, the
diffracted light from the focus monitor pattern 2605 starts from
the right end of the pattern 2605. Strictly, the start point of the
diffracted light differs depending on the arrangement of the
monitor pattern. In the 16th embodiment, the small box mark is
formed from fine patterns, and the large box mark is formed from
coarse patterns. The diffraction angle from a fine pattern is
larger than that from a coarse pattern. Thus, in FIG. 33B,
diffracted light from fine patterns is drawn. In FIG. 33B, all
diffracted light components emerging leftward from the fine
patterns must be shielded by a pellicle frame 2608. Thus, the right
end of the small box mark is set as the start point of the
diffracted light. L defined by the above equation (3) must be
determined considering this.
[0193] In the 11th to 16th embodiments, as a focus monitor pattern,
the box-in-box patterns as shown in FIGS. 21A to 21F are used. The
focus precision is measured from the relative distance between the
inner and outer patterns. However, the patterns to be employed are
not limited to them. Any pattern can be used as far as it can
shield only one of the two components of 1st order diffracted
light.
[0194] For example, assume a pattern in which the pattern pitch is
increased and the diffraction angle is decreased so both of the two
1st order diffracted light components reach the wafer. With this
pattern, even if defocus occurs, a positional shift does not occur.
When such a pattern is arranged close to the focus monitor pattern,
the focus precision can be measured from the relative distance
between this pattern and the focus monitor pattern.
[0195] Regarding measurement, an alignment inspecting apparatus
need not always be used. Any measuring apparatus may be used as far
as it can measure a relative shift between a pattern, for which
only one of the two 1st order diffracted light components is
shielded and a transfer position on the wafer is shifted due to
defocus, and a pattern, for which the diffracted light is not
shielded at all, that is, which is not positionally shifted due to
focus.
[0196] As has been described above in detail, according to the 11th
to 16th embodiments, a focus monitor pattern may be formed from two
types of patterns with different diffraction angles. One of the
two, positive and negative, diffracted light components from the
pattern with the larger diffraction angle may be shielded. Thus,
defocus can be detected from the shifts of the two types of
patterns.
[0197] In this case, the focus monitor pattern need not be
specially formed on a monitor mask. If a focus monitor pattern is
arranged outside a pattern region where a device pattern is formed,
it can be used for focus monitoring. Therefore, the focus of the
projection optics can be measured with high sensitivity and high
precision without using a special mask for focus monitoring.
[0198] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *